Earthquakes have always been a significant aspect of the design and safety of dams. This position paper deals with the seismic safety of large dams, based on experiences with large earthquakes in Japan (Tohoku earthquake, 2011, Richter magnitude 9.0), in China (Wenchuan earthquake, 2008, Richter magnitude 8.0) and in Chile (Maule earthquake, 2010, Richter magnitude 8.8). It presents ways to prevent key aspects of large dam failure under severe seismic conditions with a focus on design instead of on earthquake prediction. This is done by considering the prevention of uncontrolled rapid release of water of a storage dam under full reservoir conditions in relation to expected seismic conditions. This position paper is composed by the Committee on Seismic Aspects of Dam Design of The International Committee of Large Dams. Les tremblements de terre ont toujours été un aspect important de la conception et de la sécurité des barrages. Ce document de synthèse traite de la sécurité sismique des grands barrages, en se fondant sur l’expérience acquise lors de grands séismes au Japon (séisme de Tohoku, 2011, magnitude 9,0 sur l’échelle de Richter), en Chine (séisme de Wenchuan, 2008, magnitude 8,0 sur l’échelle de Richter) et au Chili (séisme de Maule, 2010, magnitude 8,8 sur l’échelle de Richter). Il présente des moyens de prévenir les aspects clés de la défaillance des grands barrages dans des conditions sismiques sévères en mettant l’accent sur la conception plutôt que sur la prévision des séismes. Pour ce faire, on examine la prévention d’une libération rapide et incontrôlée de l’eau d’un barrage de stockage dans des conditions de réservoir plein par rapport aux conditions sismiques prévues. Cet argumentaire est composé par le Comité sur les Aspects Sismiques des Projets de Barrages de la Commission Internationale des Grands Barrages.

Hydrology and dams are two fields that are obviously closely related. Four bulletins have so far been published by the Committee: Selection of Design Flood – Current methods, Dams and Floods – Guidelines and cases histories, Role of Dams in Flood Mitigation – A review and Integrated Flood Management. These bulletins have essentially addressed floods, the risks they represent and their significance for the concerned populations. The present Bulletin deviates slightly from this path, adopting a somewhat more technical perspective. The text consists of three chapters, conceived to be accessible to the practitioners.

From earth tectonics and meteorology to risk, responsibility, and the role of government, this comprehensive and detailed book reviews current practices in designing dams to withstand extreme hydrologic and seismic events. Recommendations for action and for further research to improve dam safety evaluations are presented.

Dams are part of human achievements that induce great benefits for society but also bear a potential risk to people, property and the natural environment. The risk of a dam rupture is extremely low and diffi cult to quantify accurately. The aim of ‘Dam surveillance’ (ICOLD Bulletin 158), is to help reduce these risks by early detection of an undesirable event. The objective of dam surveillance is to make a precise and timely diagnosis of the behavior of dams, in order to prevent undesirable consequences. Both the monitoring system and surveillance program has to be designed and should be able to detect any abnormal behaviour. ‘Dam surveillance’ (ICOLD Bulletin 158), emphasizes the following aspects: • Routine visual inspection • Special inspection • Checking and testing of Hydro-electromechanical equipment • Monitoring parameters and devices • Automation • Maintenance of ageing monitoring systems • Re-instrumentation of existing dams • Recent developments • Data management • Dam documentation management • Assessment of dam condition and behaviour • Assessment of routine dam safety monitoring programme • Prioritization of maintenance, remedial and upgrading works.

The hazard posed by large dams has long been known. Although no concrete dam has failed as a result of earthquake activity, there have been instances of significant damage. Concerns about the seismic safety of concrete dams have been growing recently because the population at risk in locations downstream of major dams continues to expand and because the seismic design concepts in use at the time most existing dams were built were inadequate. In this book, the committee evaluates current knowledge about the earthquake performance of concrete dams, including procedures for investigating the seismic safety of such structures. Earthquake Engineering for Concrete Dams specifically informs researchers about state-of-the-art earthquake analysis of concrete dams and identifies subject areas where additional knowledge is needed.

ICOLD Bulletin 150, Cutoffs for Dams, discusses foundation treatment methods using cutoff-type barriers. High emphasis is given to alluvial deposits throughout this document; however, different materials may require cutoff. The construction of cutoffs has made significant advances mainly through the development of more powerful machinery for drilling and excavation, but also through the introduction of new concepts and techniques, such as jet grouting and deep soil mixing. The following types of cutoffs are presented in this Bulletin: - Diaphragm walls - Vib walls - Pile walls - Superimposed concreted galleries - Jet grouting - Deep mixing These methods are described, and the practical application of each method is illustrated by selected case histories. These case histories also demonstrate how certain difficulties specific to a particular dam site have been dealt with. The performance of cutoffs should be monitored so that their efficiency in reducing flow and piezometric head can be evaluated. Piezometers installed in the foundation upstream and downstream of the cutoff are needed to meet this objective.