Damage progression on breakwaters

This thesis addresses depth-limited breaking wave damage on rubble mound breakwaters. Few generalized studies have been conducted on this topic. As such, no engineering methods exist for determining the deterioration rates of breakwaters exposed to sequences of depth-limited storms. These deterioration models are required for risk and reliability analyses.; A new experiment is discussed measuring incipient motion on both stone and sphere armor layers. Wave velocity measurements were made during this experiment both inside and just outside the armor layer using a laser Doppler velocimeter. Maximum vertical convective acceleration across the armor layer is shown to be proportional to the square of maximum vertical velocity. An incipient motion criterion similar to the Shields criterion for sediment motion is derived for the dominant mode of motion: vertical lift under the steep breaking-wave face. This equation is restated in terms of the stability number to provide an incipient motion criterion similar to existing stability equations. Experimental measurements are used to validate this incipient motion criterion for breakwater armor.; Previous breakwater damage experiments and measurement techniques are thoroughly reviewed. A new experiment is described consisting of seven relatively long-duration breakwater damage test sequences conducted in a flume using irregular waves. Damage measurement techniques were developed and breakwater deterioration data were acquired for breaking wave conditions. Wave height and period, water depth, storm duration and sequencing, and stone gradation were all varied systematically yielding relationships for both temporal and spatial damage development. Maximum eroded depth and length, and minimum remaining cover depth are introduced to describe the damaged profile. The mean and standard deviation of these profile parameters are shown to be a function of mean eroded area, and predictive equations are given. An equation is also provided to predict the standard deviation of eroded area as a function of mean damage. Relations for predicting temporal variations of mean eroded area with wave height and period varying with time in steps are shown to describe damage reasonably well. The prediction is shown to improve significantly if the initial profile adjustment is accounted for in the test series with relatively small cumulative damage.