Importance of dam safety

Dear ICOLD Committee Members, Dear Colleagues and Friends

I wish you good health and all the best in the New Year.

Here are a few personal comments:

In connection with the discussion of climate change, it is concluded that dams are structures, which are directly affected by these changes. If nothing is done then the safety of dams may decrease. However, if current practice of the dam industry is followed, this is not necessarily the case. Climate change is only one of the many natural and man-made hazards, which are changing with time and must be taken into account in the safety assessment of dams and which dams must be able to withstand safely.

It must be kept in mind that the ultimate goal of dam safety is that people living downstream of both a new and an old dam should feel equally safe. This implies that old and new dams must both satisfy the same minimum safety criteria. This is particularly a problem for the earthquake safety of large dams, as the seismic design criteria and seismic safety criteria have undergone important changes since many of the existing dams were built. This is, for example, true for dams built or designed against earthquakes before 1989 when ICOLD published its first guideline on the Selection of Seismic Parameters for Large Dams. Because of these developments, it is not known if older dams comply with today‘s seismic safety criteria. As all dams should satisfy the current seismic safety criteria at all times, there is an urgent need for the seismic safety evaluation of all dams that were not designed according to today‘s safety standards. The minimum design and safety criteria, which must be satisfied are those published by ICOLD. They represent the state-of-the-practice.

Today‘s seismic safety criteria not only apply to the dam body but also to safety-critical elements like gated spillways and low-level outlets, which must be operable after strong earthquakes in order to keep the water level in the reservoir at a safe limit or to lower the reservoir level to increase the safety of the dam. Moreover, the stability of slopes, whose failure may create impulse waves in the reservoir that could overtop the dam crest or block the intakes of spillways and low-level outlets must be checked for the ground motions of the safety evaluation earthquake.

An important issue is the risk classification of dams, which may vary for different countries or organisations. Risk classification is the main factor that governs the seismic design and safety criteria. As a result, the seismic safety criteria of similar dams may be different in different countries. There are also new safety requirements that concern electro-mechanical and hydro-mechanical engineers as well as geologists and geotechnical engineers involved in slope stability analyses, who may not be familiar with the current seismic safety concepts for dams.

These comments, which are related to seismic safety, apply equally to the other hazards including those due to climate change. Because of these changes in hazards, design and safety criteria and changes in the risk classification of dams, periodic reviews of the safety of dams are mandatory. If important changes have taken place, a re-evaluation of the safety may be necessary. In the case of earthquake safety, this may be needed every 20 to 40 years. As the seismic hazard and seismic safety criteria have undergone the greatest changes over the last few decades, a reassessment of the seismic safety of dams is required if not already carried out.

Some of these ideas may have been discussed before, but important tasks must be repeated.

In the past year I gave online seminars and workshops in India, China and Pakistan. It is important that the information gained from our ICOLD committee be disseminated among dam engineers and people in charge of dam safety in earthquake-prone countries or regions, and countries where large dams are being built. Like in the previous year, because of travel restrictions due to Covid-19, I mainly visited dams and run-of-river power plants in Switzerland and along the Swiss-German border.

Finally, I would like to mention that at the ICOLD Congress in Marseille in 2022 I was awarded honorary membership of ICOLD, which is a great honour for all recipients.
I would also like to thank all of you, who contributed to the work of our ICOLD committee in the past year.

With my best regards for 2023

Dr. Martin Wieland

Chairman Committee on Seismic Aspects of Dam Design (ICOLD: International Commission on Large Dams), Switzerland

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