Anton J. Schleiss
Ecole polytechnique fédérale de Lausanne (EPFL)
Hon. Président CIGB - ICOLD, Coordinator Hydropower Europe
Terrassenweg 8, CH-6048 Horw
Title of the Talk : “The Challenge of Rock Scour Assessment at High Head Spillways”
In today’s spillway design of dams there is a tendency of increasing the unit discharge of high-velocity jets leaving the appurtenant water release structures. For gated chute flip bucket (ski jump) spillways, unit discharges between 200 and 300 m 3 /s/m are not rare anymore, since the cavitation risk is mitigated by chute bottom aerators. Crest spillways for arch dams are currently designed for unit discharges from 70 m 3 /sm to 120 m 3 /sm by installing crest gates. With the latest high-pressure gate technology, mid- and low-level orifice spillways evacuate unit discharges up to 400 m 3 /s.m. Scour of rock is of concern when assessing the effect of jets released from spillways plunging onto rock foundations downstream of dams or designing plunge pools. Rock scour is a complex problem studied extensively experimentally but often in a simplified way by using granular material. Nevertheless, reliable scour prediction in rock must consider the relevant physical processes when fluctuating turbulent pressures of highly aerated flow in the plunge pool are propagating into fractured rock masses resulting in a strong fluid-air-rock interaction. In modern scour evaluation methods, the potential and extent of rock scour is determined by employing the principles of fracture mechanics and Newton’s second law. Continuing research into various aspects of turbulent flow and its interaction with rock formations refine this procedure. The main difficulties encountered when estimating scour depths are discussed, including the choice of the appropriate theory for rock scour assessment, interpretation of hydraulic model tests and prototype observations, the scour rate, and the prevailing discharge. The selection of the flood return period is addressed, for which the scour formation and the control measures have to be evaluated, as also options of measures for scour control. Finally, the challenges for dam designers are presented when answering relevant questions reading dam safety and powerhouse operation.
About the Speaker
Prof. Dr Anton J. Schleiss graduated in Civil Engineering and obtained a PhD on the topic of pressure tunnel design from ETH in Zurich, Switzerland. After having worked for 11 years with Elektrowatt (now AFRY) in Zurich, he was nominated 1997 full professor and director of the Laboratory of Hydraulic Constructions of EPFL in Lausanne. He supervised more than 50 PhD and Postdoc research projects. In 2006, he obtained the ASCE Karl Emil Hilgard Hydraulic Price as well as the J. C. Stevens Award. He was listed in 2011 among the 20 international personalities that “have made the biggest difference to the sector Water Power & Dam Construction over the last 10 years”. In 2015, he obtained the ASCE-EWRI Hydraulic Structures Medal. The French Hydro Society (SHF) awarded him with the Grand Prix SHF 2018 and IAHR in 2021 with the honorary membership. After having served as vice-president since 2012, he was president of the International Commission on Large Dams (ICOLD) from 2015 to 2018. With more than 40 years of experience he is regularly involved as a consultant and expert in large water infrastructures projects including hydropower and dams all over the world.