The present state of the art of dam engineering has been ronmental, and political factors, which, though important, attained by a continuous search for new ideas and methods are covered in other publications. while incorporating the lessons of the past. In the last 20 The rapid progress in recent times has resulted from the years particularly there have been major innovations, due combined efforts of engineers and associated scientists, as largely to a concerted effort to blend the best of theory and exemplified by the authorities who have contributed to this practice. Accompanying these achievements, there has been book. These individuals have brought extensive knowledge a significant trend toward free interchange among the pro- to the task, drawn from experience throughout the world. fessional disciplines, including open discussion of prob- With the convergence of such distinguished talent, the op- lems and their solutions. The inseparable relationships of portunity for accomplishment was substantial. I gratefully hydrology, geology, and seismology to engineering have acknowledge the generous cooperation of these writers, and been increasingly recognized in this field, where progress am indebted also to other persons and organizations that is founded on interdisciplinary cooperation. have allowed reference to their publications; and I have This book presents advances in dam engineering that attempted to acknowledge this obligation in the sections have been achieved in recent years or are under way. At- where the material is used. These courtesies are deeply ap- tention is given to practical aspects of design, construction, preciated.