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COMMISSION INTERNATIONALE DES GRANDS BARRAGES ------- VINGT-SIXIÈME CONGRÈS DES GRANDS BARRAGES Autriche, juillet 2018 ------- 3D BLOCK ERODIBILITY: REAL-TIME MONITORING IN AN UNLINED ROCK SPILLWAY CHANNEL Michael F. GEORGE Senior Geological Engineer, BGC ENGINEERING, INC. USA Nicholas SITAR Edward G. Cahill and John R. Cahill Professor of Civil Engineering, UNIVERSITY OF CALIFORNIA - BERKELEY. USA 1. INTRODUCTION Scour of rock foundations and spillways pose a significant concern for the safe and reliability operation of dams across the world. The February 2017 events at the Oroville Dam spillways in California, USA are a prime example. Knowledge regarding the mechanics of rock mass break-up resulting from hydraulic loading is still limited and has largely been deduced from scaled laboratory models and testing. This is due, in part, to the challenge of making direct observations of the rock scouring process during spill events from actual dam and spillway sites. Due to these challenges, nearly all studies on rock erodibility have focused on laboratory testing using simplified rock block geometries (i.e., rectangular/cubic blocks) under idealized flow conditions [1-14]. Extrapolation of the findings of such studies to field conditions can be challenging given the highly irregular 3D geologic structure often encountered at specific sites which, as many rock mechanics practitioners are aware, significantly influences block/rock slope stability. 1492