Riprap Stability Under Wave Action

Abstract

A mathematical model is developed to predict the flow characteristics in the downrush of regular waves and the critical condition for initiation of movement of armor units on the slope of a coastal structure. The analysis of water motion on the slope is based on the standing‐wave solution of the finite‐amplitude shallow‐water equations with an implicit account of the effects of wave breaking. This simple model neglects the effects of permeability, bottom friction and water depth. In addition, use is made of an empirical runup relationship. A stability analysis of armor units is performed including the drag, lift and inertia forces acting on an armor unit which vary along the slope with time over the period of wave downrush. Comparison is made with the largescale test data on riprap stability from an earlier study. The predicted critical stability number follows the same trend as the observed zero‐damage stability number, although the agreement is qualitative.