Performance of RCC used for overtopping protection and spillways

Abstract

Roller-compacted concrete (RCC) has become the most widely accepted method for providing safe overtopping protection for embankment dams in the United States. The concept consists of placing horizontal layers of erosion resistant RCC on the downstream slope of existing dams to increase spillway capacity during extreme rainfall events. Since the first earth dam with an RCC overlay was constructed in 1984, more than 130 such projects have been put in service. Because most of these hydraulic upgrades were designed to accommodate rare flow events, there was little information initially available of their actual performance when overtopped. With more RCC overtopping protection in service, there are now more examples of floods in excess of the 1 in 100 year event overtopping RCC protected dams. This paper will present data on the performance of RCC overlay projects when overtopped and lessons learned from these actual examples.