Comparison and Evaluation of Different Riprap Stability Formulas Using Field Performance

Abstract

Five riprap stability formulas have been compared and evaluated using the field performance of several riprap across the La Grande Hydroelectric complex. Four of these formulas were developed from regular wave tests (Hudson, Sherbrooke University, Koev, and Bertram formulas), while the other formula was developed from irregular waves tests conducted by Van Der Meer. For each site, the stone size required to resist the maximum wave experienced by the riprap was calculated and compared with the measured stone size. The comparison showed that the Hudson, Sherbrooke University, and Koev formulas give a realistic picture of the observed performance. In the case of riprap with significant damage, the stone sizes calculated by these three formulas were always larger than those measured in the field. When used in its general form, as presented in the literature, the Van Der Meer equation does not fully predict the observed behavior. However, it constitutes a good prediction tool if the permeability factor and the start of damage criteria proposed by Van Der Meer are adjusted. The Bertram formula has been found to underestimate the stability.