It is an honor and a pleasure to present the closing address at this outstanding Symposium. I’m sure you all will agree that our expectations in following the invitation from Osaka were more than fulfilled. I have learned a lot, and it was so good to meet colleagues and friends and to have had the opportunity for exchanges with them.

Permit me to focus on the central topic of our Special Symposium II, “Lessons from Recent Tainter Gate Failures” and to start with a personal remark. I have often been marveling about Professor Ishii’s untiring pursuit of that subject since the later 70ies and particularly during the past 6 years. Today I cannot but express my deep respect for the outcome of this effort and for its significance. To be sure, the safety of these gates ranges among the most important concerns of hydraulic engineers in view of the great number of installations that utilize Tainter gates worldwide. So I was not surprised when I learned that the U.S. Bureau of Reclamation called on Professor Ishii in July 1995 asking him for consultation on the failure of one of the 50-foot-high Tainter gates of Folsom dam. Fortunately, the incidence did not cause losses of human lives as in cases of similar catastrophes; but the loss of the greatest part of precious water stored behind Folsom dam for the supply on Northern California was serious enough.

I have known Professor Ishii since his participation at the 2nd International Vibration Symposium in Karlsruhe 1979 and since his time as a visiting Humboldt Research Fellow at our University in 1983/84. For more than 25 years he has now been studying flow-induced gate vibrations, and he has done that disregarding his health, until in 1992 he was diagnosed with an early stage of cancer. In one of his reports on the Folsom-dam gate failure he remarked that luckily he lived on to help uncover the causes of this failure. I hope he’ll permit me to quote from one of these reports: “The 3 months since the gate failure”, he writes, “have passed in an incredible flurry of activity; but for [me] these 3 months have been the best of [my] life.” (Looking back on the 3 months preceding this conference, I’m afraid, he could undoubtedly make a similar statement today. ? Take good care of yourself, dear Noriaki, in the months to come!)

But be assured, it was worth your while! For the discovery of a new and most dangerous instability of Tainter gates, you and Keiko Anami are to be highly congratulated! Congratulations not only for the detective kind of way in which you applied forensic observations, field tests, computer simulations etc. to prove that hydrostatic loading and friction alone could not have destroyed the Folsom-dam gate, as was initially suspected; but compliments also to you and Keiko-san for your impressive theory on a previously unknown dynamic instability of Tainter gates, complete with convincing verifications by model tests and the prove that an instability of that type must have been involved in the Folsom-dam catastrophe.

As if all this hadn’t been enough, you insisted that there should be additional proof by the evidence from field tests. So you, with the help of Keiko-san, planned and prepared for such tests, not minding that they could only be carried out a few days prior to this symposium! All of us who know of your tireless zeal and determination, and who also know about the frustrations possible with field tests, we do share your joy and pride. You certainly deserve the victor’s laurel that the successful field tests have bestowed on you!

After all, the importance of your discovery of a new gate instability rests in the fact that its danger ? like in case of time bombs ? may go undetected for 30, 40, ? even 50 years as the Folsom dam failure has demonstrated. Since the newly found instability can also lead to hard in contrast to soft excitation, gate vibrations may be excited only if a certain threshold amplitude is initially exceeded. At the Folsom-dam gate 3, this vibration-triggering event occurred most probably after an intermediate blockage of the gate during the lifting process (caused by excessive friction) was suddenly overcome. Therefore, measures that exclude excessive friction ? as claimed by the Bureau of Reclamation in its Forensic Report of Oct. 17, 1996 ? may well have been necessary to reduce extra static loading on the radial arm structure. But they will also reduce structural damping and thus increase the danger for self-excited gate vibration! To be sure, the triggering amplitude for such vibrations to come about could be generated in other ways, e.g. by waves induced in cases of landslides into the reservoir, by boats or logs bumping into a gate, or by obstacles intermediately jamming the gate lifting or closure.

I can only hope that managers and engineers responsible for the operation and maintenance of Tainter gate installations will immediately take notice and action. In particular I hope the Bureau of Reclamation will update its Forensic Report, as well as subsequent publications and memos based on it. But of course, these new findings call also for a revision of many other publications that serve as design guides. A case in point is the 1994 IAHR Hydraulic Design Manual on Flow Induced Vibrations by Don Rockwell and myself; it’s high time for its first revised edition!

Let me come to the main purpose of this address, the closure of our meeting. I’m sure I speak in the name of all participants if I extend our sincere thanks to all of you at this University who helped to organize this great Symposium and make our stay here so pleasant. We have learned a great deal from the various presentations and very much enjoyed the wonderful Japanese hospitality. It was a great meeting! Thank you, Professor Ishii, Professor Sasaki, and all around you who made this possible and who contributed to its success!

Please convey our gratitude to Dr. Fukuda and the University Board of Directors for sponsoring this Symposium and for the generous support to the contributors from abroad; and, last not least, our thanks also to your many friendly assistants, most of them graduate students of this university. It was an excellent idea to broaden the scope of the Symposium topic to include FIV of gates other than Tainter gates, and we are indebted to all invited contributions for bringing us up to date on the latest advances in their research fields.

We congratulate this University to its 40^th Anniversary and wish for continued success, and good fortune and prosperity for the future!