The increase in Kt for waves less than about 1 m in height is caused by wave transmission
through the structure. For small waves, the dominant mode of wave transmission is through the
structure. If the scale of disturbance is large compared to the void spaces in the stone, the
transmission process is inefficient. As the wave height becomes smaller, the transmission process is
more efficient and produces larger values of Kt. However, the relatively small waves do not create
significant changes in the shoreline position.
Figure 6 plots the percent difference between the constant and variable Kt simulation predictions
for the Atlantic wave climate by month for a 1-year interval. The results are representative of the
Gulf of Mexico wave climate. The application of the variable Kt results in 10-30% less average
shoreline advance behind the structure. Therefore, shoreline planform predictions can be
significantly different in applying a time-dependent wave transmission and are expected to be more
accurate than if applying a constant value of Kt or omitting wave transmission altogether.
F2 b Mar
A8 g S9 p O0t
Fig. 6. Percent difference in shoreline change behind emergent near- surface structure
between constant and time-dependent Kt calculation methods by month
Emergent High Structure
Figure 7 shows the 4-year shoreline position change behind a 300-m long detached breakwater
located 300 m offshore for both wave climates. The crest of the structure is at elevation +6 m msl.
The average shoreline change behind the structure predicted by the variable Kt simulation is less
than 5% greater than the constant Kt simulation for both wave climates.
Figure 8 plots the percent difference between the constant and variable Kt simulation shoreline
change predictions for the Atlantic wave climate by month for a one-year period. The application of
the variable Kt results in no more than a 5% difference in the predicted average shoreline change
behind the structure. Results are similar for the Gulf of Mexico wave conditions. The high crown
elevation allows wave transmission only through the breakwater, and changes in water level have no
effect. The average Kt for both wave climates is about 0.2. Transmitted waves are small, and any
difference between constant and variable Kt computations is small resulting in relatively little
difference in shoreline change.
Wamsley et al