Effect of Nominal Stone Diameter on Stability of Reshaping Berm Breakwaters

Berm breakwaters are structures that reshape under waves action and reach to a stable profile. In this
type of breakwaters the units of the armor layer are allowed to move in order to take a final form
without changing the serviceability performance of the structure. The remaining berm width - after
rescission - is the main criterion for stability of these structures. If the rescission become more than the
initial berm width, the breakwater will be unstable and failure will occur.
In this paper the effect of nominal diameter on stability of reshaping berm breakwaters is investigated
by experimental studies. In order to consider the effect of this parameter in comparison with other
parameters, 120 tests have been carried out in the wave flume of Tarbiat Modares University
Hydraulic Laboratory. The waves in all tests are irregular waves conforming JONSWAP spectral
energy. The amount of is assumed for graining.
Results indicate that water depth has a considerable effect on berm rescission comparing to nominal
diameter. However, the initial berm width has the same effect as nominal diameter. The results also
show that by raising the position of berm to water level, rescission effect is reduced. On the other hand
by decreasing nominal diameter and increasing the initial berm width the same percentage of
rescission could be expected.