| Dam safety
stability of cofferdams. In the case of diversion tunnels, seismic considerations are especially important for the inlet portals. Seismic loading refers to the application of seismic oscillations on a structure and constitutes a primary load consideration for hydraulic structures. Bulletin 148 of the International Commission on Large Dams (ICOLD)1
states: “For critical construction phases and temporary
structures such as cofferdams, retaining structures etc. it is also necessary to check the earthquake safety. The return period of such earthquakes depends on the type of structure, the duration of its use or the duration and seismic vulnerability of the structure during critical construction stages and the consequences of its failure”.
Liu et al.2 demonstrated that a construction
earthquake could severely affect a cofferdam in a high seismicity region, potentially compromising its stability and serviceability. Huang and Liu3
reported
severe damage to temporary works at Upper Trishuli-3A hydropower project in Nepal during the 2015 Gorkha earthquake (magnitude of 7.8), which occurred while the project was under construction. The dam site is located approximately 70km from the epicentre. At present, there is no international standard specially
addressing the seismic design of river diversion works, leaving fundamental question unanswered, such as when to consider construction earthquakes and how to define appropriate design parameters, which have been perplexing dam engineers. In practice, the absence of national and international standards has led to diverse criteria and project-specific approaches, resulting in inconsistent design quality and varying levels of seismic risk management for temporary works. To bridge this design gap, the author aims to address
the problem, bring attention to this overlooked issue and offer a preliminary framework. This paper proposes design criteria which may serve as a useful starting point for consistent and robust seismic design of temporary river diversion structures.
design of temporary works It is well known that the design of temporary works differs significantly from that of permanent works. These differences must be considered when formulating design methods and selecting design parameters. ● Shorter service life: Temporary works typically have much shorter service lives than permanent works. For instance, a cofferdam usually serves for 3 to 5 years, whereas the prescribed lifespan of a main dam is 100 years. It is very rare for a cofferdam to be in use for 8 to 10 years. Consequently, exposure of cofferdams to earthquake events is less than for permanent structures.
2. Challenges associated with seismic
● Limited Impact on permanent structures: Failure of temporary works may delay the construction schedule, but not necessarily compromise the integrity of permanent structures such as concrete dams.
● Controlled use: Temporary works are used within controlled construction sites for the project construction and are not accessible to the public. Cofferdams being lower in height than main dams, are often subject to lower performance expectations under seismic conditions.
These factors likely contribute to the lack of relevant
. However, this mindset poses several challenges at least on the following counts: ● Lack of awareness: Contractors and clients may be unaware of the need for seismic design in temporary works, leading to seismic risks being overlooked or underestimated. Allowances of seismic design for temporary works may not be included in tender documents.
● Limited focus during design: Designers of permanent works may account for construction methodology but often give little attention to the seismic resilience during the construction phase.
● Responsibility delegated to contractor: In most dam and hydropower projects, the design, construction and operation of temporary works are the sole responsibility of the contractor. The capacity of components is often quantified by the contractor’s in-house analysis and testing, with seismic loading frequently omitted from design, detailing, and testing processes.
● Cost-driven omission: Contractors may neglect seismic requirements for the temporary structures to minimise project costs and shorten construction timelines. The supervision of temporary works is often perfunctory, further compounding the issue.
● Lack of seismic monitoring: While permanent structures are subject to rigorous seismic monitoring, there is little to no observation of the performance of temporary works during earthquake events. This absence of monitoring work makes it difficult to improve the seismic design of such structures. Despite their temporary nature, cofferdams are water
retaining structures and thus relevant to public safety. Many cofferdams are 15m or higher – some even approaching 100m – which can be classified as large dams according to ICOLD’s World Register of Dams. Cofferdams may encounter earthquakes, causing damage or collapse and thus pose a risk to public safety. Cofferdam failures may cause loss of life among downstream residents and construction personnel, significant property damage and construction delays. This is particularly critical for cofferdams with long service lives, where a failure could lead to severe consequences. In such cases, the design should be based on longer return periods to ensure sufficient resilience.
www.waterpowermagazine.com | January 2026 | 25
standards/codes associated for seismic design of temporary works. Some standards even suggests that “As cofferdams are temporary structures, generally earthquake factor need not be considered in the designs”4
Author information
Chongjiang Du is a key expert in dam engineering with Lahmeyer International Ltd., Germany. He received his bachelor’s degree in civil engineering from Dalian University of Technology, China, and his master’s degree from Tsinghua University, China. He worked as an assistant professor at the Karlsruhe Institute of Technology (former University of Karlsruhe), Germany, where he was awarded his Dr.-Ing. title. He started his career in 1982 with more than 40 years of experience as a designer and consultant in dam engineering, specializing in concrete dams and concrete technology, including conventional concrete and RCC dams. He is also one of the primary authors of ICOLD Bulletin 177, “Roller-Compacted Concrete Dams”, 2020. He was involved in design/ consult, construction supervision, research and technical administration of various concrete dams. He presently works on several concrete dam projects.
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