Field Performance and Analysis of Steep Riprap

The performance of riprap with a slope on the order of 1.5:1 to 2.3:1 was evaluated at 14 different dam sites in the James Bay Territory in Northern Québec. The field investigations included gradation measurement at each site and have allowed a back analysis of the performance using the wave height experienced by the riprap since reservoir filling. The wave prediction method recommended by the U.S. Army Corps of Engineers in 1984 and the Hudson stability formula have allowed a back analysis in good agreement with the observed field performance for regular gradation riprap. For riprap containing a significant portion of fine material, the observed damage was always more severe than predicted using the median weight. The results of the study show that for steep slopes the inclusion of fine stones in the riprap is detrimental to the stability.