Armor Stability Based on Wave Momentum Flux

In this paper, new generalized breakwater armor stone stability equations are derived based on the assumption that the maximum wave momentum flux is proportional to the maximum wave forces on armor units. Stability equations are derived for uplift, sliding, and rolling incipient motion. A generalized empirical stability equation is proposed that characterizes these three cases of instability. This equation is fit to small-scale laboratory data yielding two stability equations distinguished by whether the waves are surging or plunging on the structure. In the new stability relations, wave-structure interaction and nearshore nonlinear wave transformation are separate, overcoming a major limitation of previous stability relations. The new relations clearly illustrate the influence of water depth and wave period on stability. The momentum-based approach illustrates why minimum stability is observed for steep plunging breakers in shallow water.